Stoichiometry of An( III)- DMDOHEMA complexes formed during solvent extraction

N,N-Dimethyl,N,N-dioctylhexylethoxymalonamide (DMDOHEMA) is used to separate An(iii) and Ln(iii) from fission products in several liquid-liquid extraction processes that aim at recycling actinides. The stoichiometry of the extracted complexes is important for a complete understanding of the processes. The presented work focuses on the complexation of Cm(iii) with DMDOHEMA studied by TRLFS in mono- and biphasic (solvent extraction) systems. The formation of [Cm(DMDOHEMA)(n)](3+) (n = 1-3) in 1-octanol containing 1.7 mol L-1 of water with log(1) = 2.6 +/- 0.3, log(2) = 4.0 +/- 0.5, log(3) = 4.3 +/- 0.5 was confirmed. In addition, fluorescence lifetime measurements indicated the formation of a 1:4 complex. Furthermore, solvent extraction experiments were performed, varying the proton and nitrate concentrations. TRLFS measurements of organic phases confirmed the existence of two species, [Cm(DMDOHEMA)(3)(NO3)(H2O)(1-2)](2+) (dominant at high proton and nitrate concentrations) and [Cm(DMDOHEMA)(4)(H2O)](3+) (dominant at low proton and nitrate concentrations). To support the proposed stoichiometries, vibronic side-band spectroscopy (VSBS) was employed, allowing the observation of vibrations of functional groups coordinated to the probed metal ion. Clear differences between the vibronic side bands of the 1:3 and 1:4 complex in the range of 900-1300 cm(-1) were observed. Vibrational spectra calculated by DFT complimented the experimental data and confirmed the proposed stoichiometries. They revealed a monodentate coordination mode of the nitrate and two water molecules in the 1:3 complex.